Shielding braid termination for a shielded electrical connector

ABSTRACT

The present invention relates to shielded electrical cables and shielded electrical connectors to be affixed thereto, and in particular to the termination of the shielding braid provided at the electrical cable. According to the present invention, a shielding termination structure for engaging a shielding ( 104 ) of a shielded cable ( 100 ) having an insulated conductor ( 102 ) that is encompassed by said shielding is provided, said shielding termination structure ( 110 ) comprising: an electrically conductive shield body ( 114 ) for establishing an electrical connection between said shielding ( 104 ) and an electrically conductive interface ( 118 ), fixing means ( 126 ) for securing said shield body ( 114 ) at the interface ( 118 ); an electrically conductive spring element ( 120 ) that is arranged between said shield body ( 114 ) and the interface ( 118 ) for establishing the electric contact in a compressed state of the spring element ( 120 ).

BACKGROUND OF THE DISCLOSURE

The present invention relates to shielded electrical cables and shieldedelectrical connectors to be affixed thereto, and in particular to thetermination of the shielding braid provided at the electrical cable.More specifically, the present invention can be applied for sealedelectrical connections which are for instance necessary with automotiveapplications.

When terminating a shielded electrical cable, it is common toelectrically couple the shielding braid of the cable to a shield memberof an electrical connector or electrical device. One way ofaccomplishing this is to attach the braid directly to the shield bywelding or soldering. Another method is to include a crimp ring thatfits above the braid of the cable and may be crimped thereto such thatthe braid is positively retained. After crimping, the crimp ring must beconnected with the connector shield. Radially expanding resilientelements may be used to establish the connection between the crimp ringand the housing. Another known solution is to crimp the braid directlyto the connector housing. This may be accomplished by providing a flangethat extends from the shield that would fit beneath the braid andprovide a crimp ring thereover, that when crimped tightly fastens thebraid therebetween. It is also known to join the braid to a shieldflange directly as described above, but rather than using a crimp ring,a second ring is used that is press fit thereupon, thereby captivatingthe braid between the two rings.

However, most known solutions suffer from the disadvantage that they arenot sufficiently robust to withstand the vibrations and temperaturechanges in the automotive application field. Moreover, in many cases theconnection between the shielded electrical cable and the shield of forinstance, a housing has a too high electrical resistance. On the otherhand, soldering connections are making the assembly much more difficultand expensive.

SUMMARY OF THE DISCLOSURE

The object underlying the present invention therefore can be seen inproviding a shielding termination structure having a low electricalresistance which can be mounted in a particularly easy way and allowsthe connection of the shielding of the cable to a grounded interfaceeven under extreme ambient conditions. This object is solved by thesubject matter of claim 1. Advantageous embodiments are the subjectmatter of the dependent claims.

According to the present invention, a shielding termination structurefor engaging a shielding of a shielded cable having an insulatedconductor that is encompassed by said shielding is provided. Theshielding termination structure comprises an electrically conductiveshield body for establishing an electrical connection between saidshielding and an electrically conductive interface. Fixing means areprovided for securing said shield body at the interface. According tothe present invention, an electrically conductive spring element isarranged between said shield body and the interface for establishing theelectrical contact in a compressed state of the spring element.

This solution has the advantage, that the shield body can be designed tohave a low bulk resistance through using a high conductivity materialand by having thicker sections than normally associated with stampedferrules. The spring element provides a high normal force low resistanceconnection. The achieved normal forces can amount up to 100 N.Furthermore, the spring element will absorb assembly tolerances therebyeliminating the need for tight manufacturing tolerances and thusreducing the fabrication costs. Furthermore, the spring element willensure high pressure contact that is maintained even under conditions ofvibration, differential movement due to thermal expansion or loads dueto applied cable strain.

According to the present invention, the shield element can be fabricatedas a machined part, therefore it is easy to manufacture from aconductive material that is electro-chemically matched to a particularinterface and spring element, thereby minimizing galvanic corrosionpotential, which would be especially advantageous if the sealing failed,or the application was not sealed by design.

According to the present invention, the spring element is compressed ina direction along the cable axis. Such spring elements which possess anaxial resilience can be helical springs, compressible elastic materialsor wave spring washers. An important idea of the present invention isthat the electrical contact between the interface and the shield body isestablished via the spring element. The spring element therefore has toprovide a high electrical conductivity either by being fabricated from ametal or a metal filled plastic material.

A particularly space saving and economic way of fabricating the springelement, however, is to use a wave spring washer.

Wave spring washers can be made from prime quality spring steel,stainless steel, copper and other materials which are readily availablein standard sizes. Wave washers are wavy metal washers designed to offera compensating spring force and maintain a load or take up shock. Theyare formed by a disc of irregular shape which when loaded deflects, andacts like a spring, thereby providing a pre-load between two surfaces.

The number of waves around the circumference can be two, three or evenmore. The spring rate is proportional to the number of waves raised tothe fourth power. Wave washers are generally preferred as a cushionspacer between parts on shafts or to take up probable deviations inassembled parts. For the present invention a significant advantage canbe seen in the fact that in the compressed state a wave spring washerallows high normal forces resulting in a low resistance contact, becausefrom an electrical connector theory point of view the actual contactarea is solely governed by the normal force and relative hardness of thecontacting materials which results in true contact via relatively smallmicro-asperities, not the apparent projected area.

According to an advantageous embodiment of the present invention, theshield body is formed as an essentially tube shaped sleeve havingretaining means for securing said spring element at the shield body.Thereby, it can be guaranteed that the shield body and the springelement can be preassembled as a shielding termination structure and beheld on stock without the danger of losing the spring element. In thecase of a wave spring washer, a particularly effective way of retainingsame at the shield body is to provide a circumferential groove whichaccommodates the spring element.

In order to allow a facilitated assembly of the spring element at theshield body, a chamfered region can be provided at a front face of theshield body. For the assembly, the spring element is then slipped overthe chamfered region and accommodated within the retaining means. Thespring element preferably also has a slit in order to be opened radiallyfor assembly.

According to a further advantageous embodiment of the present invention,the shield body has a shielding connection region which is formed as abushing that can be encompassed by the cable shielding. In particular,when the cable shielding is formed by a braid, this allows a lowresistance connection by loosening the braid only far enough to allow atight fit around said bushing.

According to a further advantageous embodiment, the shieldingtermination structure further comprises a fastening ferrule for fixingthe shielding onto the connection region of the shield body. Such adesign allows a very secure fixing even under rough ambient conditions.The fastening ferrule can either be provided as a separate part or canbe formed integrally with the rest of the shield body. The embodiment,where the fastening ferrule is fabricated as one part with the shieldbody offers several advantages. Firstly, the assembly process isfacilitated because no separate fastening ferrule parts have to behandled. Furthermore, such a one part structure reduces the electricalresistance between the shielding braid and the shield body. Existingdesigns crimp the cable shield between an inner and outer ferrule, inthe integrated design option, the inventive shield body integrates thesetwo components.

In order to ensure that the cable shield is correctly located, in theintegrated design option the shield body may include an inspection holefor monitoring the position of the cable shield.

The mechanical and electrical connection between the cable shield andthe connection region of the shield body can be achieved by crimping,welding or soldering the fastening ferrule onto the connection region.Other known techniques for fixing a fastening ferrule around theshielding braid are of course also usable.

In order to provide a strain relief, an axial dimension of the fasteningferrule may be chosen to be longer than the connection region so thatthe fastening ferrule can be brought into direct contact with the cable.In particular, the ferrule can have a length that allows a crimping ontothe cable jacket.

According to a preferred embodiment of the present invention, the shieldbody comprises a circumferential collar which is formed in a way that byfixing the shield body at the interface, a contact surface of the collaris brought into a circumferential large area contact with the interfacevia the compress spring element. Such a collar allows that theelectrical contact is directly formed when attaching the cable to theinterface.

A particularly easy way of producing a shield body with a low electricalresistance is to fabricate the shield body as a turned, cast or mouldedpart either from a metal, such as aluminum, or from a conductive plasticmaterial.

As already mentioned, the shielding termination structure according tothe present invention is particularly suitable for applications where asealed electrical connection has to be provided. Consequently accordingto a preferred embodiment, at least one sealing is provided forprotecting the electrical connection between the shield body and theinterface against ingress of dust or water.

In order to fix the cable in a particularly easy and secure, albeitdetachable manner to the interface, said fixing means comprises at leastone screw coupling. If the screw axis is along the axis of the cable andtherefore along the axis in which the compression forces are exerted bythe spring element, very effective force transmission can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

For better understanding of the present invention, same will beexplained in the following based on the embodiments shown in thefigures. Corresponding parts are given corresponding reference numeralsand terms. Furthermore, those features or combinations of features,which show or describe different embodiments, may form separateinventive solutions in themselves. The invention will now be describedby way of example with reference to the drawings, wherein:

FIG. 1 is a partly exploded perspective view of a field connector for ashielded electrical cable using the inventor shielding terminationstructure;

FIG. 2 is a longitudinal cut of the completely assembled connectoraccording to the embodiment of FIG. 1;

FIG. 3 is a perspective, partly exploded view of a sealed electricalconnector for a shielded electrical cable according to a secondembodiment;

FIG. 4 is a longitudinal cut through the fully assembled connectoraccording to the embodiment of FIG. 3;

FIG. 5 is a side view of the inventive electrical connector in apreassembled state before mounting same onto an interface;

FIG. 6 is a perspective view on the connector arrangement of FIG. 5;

FIG. 7 is a cut perspective of a shield body according to a firstembodiment as shown in FIG. 1;

FIG. 8 is a top view onto the shield body of FIG. 7;

FIG. 9 is a cut perspective of a variant of the embodiment of FIG. 7;

FIG. 10 is a front view of the shield body according to a secondembodiment as shown in FIG. 3;

FIG. 11 is a cut perspective of the shield body of FIG. 10.

The partly exploded view of FIG. 1 shows a connector for a shieldedcable 100 according to a first embodiment of the present invention. Theshielded cable 100 comprises a center conductor 102 which is separatedfrom a surrounding shielding braid 104 by means of an insulating layer106. A cable jacket 108 which insulates the shielded cable 100 isremoved to expose the shielding braid for being contacted by theinventive shielding termination structure 110.

DETAILED DESCRIPTION OF THE DRAWINGS

The center conductor is electrically contacted by means of a terminal112. However, the particular shape of this terminal 112 is irrelevantfor the inventive shielding termination structure.

According to the present invention, a shield body 114 is provided whichis for instance, formed as a turned part from aluminum. In a connectionregion 116 this shield body 114 can be brought into contact with theshielding braid 104 for connecting the shield body 114 to an interface118, which is shown in FIG. 1 as a separate part, but in fact in mostcases will be integrally formed with a housing of an electroniccomponent. The inventive shielding termination structure furthercomprises a wave spring washer 120. The wave spring washer 120 isaccommodated within a groove 122 that retains the wave spring washer 120in a preassembled state when a connection to the interface 118 is notyet established.

As becomes more apparent from FIG. 2, according to the first embodimentof the present invention, the shield body 114 is formed in a way that itintegrally comprises a connection region 116 that can be encompassed bythe cable shielding 104 and an integrated fastening ferrule 124 whichfixes the shielding braid 104 to the connection region 116. Thefastening ferrule 124 here is dimensioned in a way that it is longerthan the connection region 116 and therefore can be brought into directcontact with the cable jacket 108. According to the present invention,the spring element 120 is compressed in an axial direction when theshielding termination structure 110 is attached to the interface 118. Inorder to exert the necessary mechanical pressure, screw couplings 126are provided between the shielding termination structure and theinterface 118. In the compressed state, the wave spring washer 120establishes a low impedance electrical contact between the shield body114 and the interface 118 via contact points made on crests of the waveform.

In the present arrangement, the interface 118 also defines a boundary128 between the wet and dry regions. In FIG. 2, the left hand sideregion belongs to the possibly dust and water containing ambience,whereas the right hand side is associated with the dust free and dryinner region of an electronic component.

In order to protect the electrical connection between the shield body114 and the interface 118 against ingress of dust or water, sealings areprovided. The first sealing 130 is arranged on a housing 134 thataccommodates the shield body 114 and directly seals against theinterface 118. A second seal 132 is provided for sealing the connectionof the housing 134 and the cable jacket 108. The second sealing is heldin place by means of a cap nut as this is known in the art.

Finally, the screw coupling 126 is provided with a compression bush 136.

The connection between the shielding braid 104 and the connection region116 is established by crimping the integrally formed fastening ferrule124 onto the connection region 116. An opening in the fastening ferrule124 serves as an inspection hole and allows an optical control whetherthe shielding braid is positioned correctly.

It is clear for a person skilled in the art that other techniques forfixing the fastening ferrule to the braid 104 may also be employedwithout departing from the idea of the present invention, such assoldering, welding or pressing lances which are provided on thefastening ferrule into the shielding braid 104.

A second embodiment of the present invention will be explained withreference to FIGS. 3 and 4. According to this embodiment, the fasteningferrule 124 is provided as a separate metal bushing. This embodiment hasthe advantage that for the connection region 116 and the ferrule 124different materials can be chosen. The connection region 116 and thecomplete shield body 140 are made from a material that has aparticularly good electrical conductivity. The fastening ferrule 124, onthe other hand, may be formed from a metal that can be fixed to theshielding braid in an optimized way by crimping, soldering or welding.Also when using lances that are bent inward towards the shielding braid104, the separate structure of the fastening ferrule is advantageous.

According to an advantageous embodiment of the present invention, theshield body 114 has a circumferential collar 138, which in the mountedstage is pressed against the interface 118, thereby compressing the wavespring washer 120 in an axial direction and establishing an electricalcontract between the shield body 114 and the interface 118.

FIGS. 5 and 6 show the shielding termination structure 110 according tothe present invention when mounted on a cable end before being connectedto the interface. It is particularly advantageous that the shield body114 has a groove 122 for retaining the wave spring 120 and therebypreventing a loss of the wave spring washer 120. A chamfered region 140which is provided at the front face of the shield body 114 facilitatesthe assembly of the wave spring washer 120. Of course, the wave springwasher 120 can also have a slit that allows a radial extension whenslipping the wave spring washer 120 into the groove 122.

FIGS. 7 to 9 show two variants of the shield body 114 according to thefirst embodiment having an integrally formed fastening ferrule. Thesetwo variants differ by the geometric dimensions of the fastening ferrule124. In FIG. 7 the fastening ferrule 124 has a length which is longerthan the connection region 116, thereby allowing a direct fixing of thefastening ferrule also onto the cable jacket and thereby providing astrain relief. An inspection hole 142 allows the visual control whetherthe shielding braid is mounted correctly before applying the crimpingforces to the fastening ferrule 124.

In FIG. 9 the fastening ferrule 124 and the connection region 116 areformed to be flush with each other. This variant is particularlyadvantageous when the available space is small.

FIGS. 10 and 11 illustrate the shield body 114 according to the secondembodiment which uses a separate bushing as the fastening ferrule 124.This embodiment amongst other advantages allows a particularly simplestructure of the shield body 114. Toward the cable end which isconnected to the terminal 112, the shield body 114 comprises a taperedregion 144 which allows bending movements of the cable without damagingthe insulating layer 106 when mounting the terminal to the electroniccomponent (not shown in the FIGS).

The present invention provides a low resistance electrical connectionbetween a cable shield and a connector interface which may in particularbe of importance for high voltage connectors in the automotiveapplication field. Two design variants are provided. The problem ofconnecting to the cable shield is solved by either crimping the cableshield into a recess within the shield body on the integrated option or,on the separate option, between a separate shield body and a ferrule.The problem of connecting the shield body to the interface of anelectronic component is solved by the use of a wave spring washer. Thus,a high pressure contact can be maintained under conditions of vibration,differential movement due to thermal expansion or loads due to appliedcable strain. Moreover, the wave spring will absorb assembly toleranceseliminating the need for tight manufacturing tolerances. Generally, thepresent invention may be used for any application where a connection toa cable shield is required.

Reference Numeral Description 100 Shielded cable 102 Center conductor104 Shielding braid 106 Insulating layer 108 Cable jacket 110 Shieldingtermination structure 112 Terminal for the center conductor 114 Shieldbody 116 Connection region 118 Interface 120 Wave spring washer 122Groove for retaining wave spring washer 124 Fastening ferrule 126 Screwcoupling 127 Boundary between wet and dry ambience 130 First sealing 132Second sealing 134 Housing 136 Compression bush 138 Collar 140 Chamferedregion 142 Inspection hole 144 Tapered region

What is claimed is:
 1. Shielding termination structure for engaging ashielding of a shielded cable having an insulated conductor that isencompassed by said shielding, said shielding termination structurecomprising: an electrically conductive shield body for establishing anelectrical connection between said shielding and an electricallyconductive interface, the shield body including a collar and aconnection region, and a portion of the shielding extending over theconnection region; fixing means for securing said shield body at theinterface; and an electrically conductive spring element that isarranged between said shield body and the interface for establishing theelectric contact in a compressed state of the spring element, whereinthe collar is brought into a circumferential large-area contact with theinterface via the compressed spring element; and wherein the shield bodyis formed as an essentially tube-shaped sleeve having retaining meansfor securing said spring element at the shield body.
 2. Shieldingtermination structure according to claim 1, wherein said spring elementcomprises a wave spring washer.
 3. Shielding termination structureaccording to claim 1, wherein at least one sealing is provided forprotecting the electrical connection between said shield body and theinterface against ingress of dust or water.
 4. Shielding terminationstructure according to claim 1, wherein said fixing means comprises atleast one screw coupling.
 5. Shielding termination structure accordingto claim 1, wherein the spring element is intermediate the collar and anaxial end of the shield body, the axial end facing the interface. 6.Shielding termination structure according to claim 1, wherein saidretaining means is formed by a circumferential groove for accommodatingsaid spring element.
 7. Shielding termination structure according toclaim 6, wherein a chamfered region is provided at a front face of theshield body for facilitating the assembly of said spring element. 8.Shielding termination structure according to claim 1, wherein theconnection region is formed as a bushing and is configured to beencompassed by the cable shielding.
 9. Shielding termination structureaccording to claim 8, further comprising a fastening ferrule for fixingthe shielding on the connection region of the shield body.
 10. Shieldingtermination structure according to claim 9, wherein the shielding isfixed on the connection region of the shield body by means of acrimping, welding or soldering connection between the fastening ferruleand the connection region of the shield body.
 11. Shielding terminationstructure according to claim 9, wherein an axial dimension of saidfastening ferrule is chosen to be longer than the connection region, sothat said fastening ferrule can be brought into direct contact with thecable.
 12. Shielding termination structure according to claim 9, whereinsaid fastening ferrule is integrally formed with the shield body. 13.Shielding termination structure according to claim 12, wherein saidfastening ferrule comprises at least one inspection hole for visualconfirmation of a correct position of the shielding.
 14. Shieldingtermination structure according to claim 1, wherein the shield body isfabricated as a turned, cast or molded part.
 15. Shielding terminationstructure according to claim 14, wherein the shield body is fabricatedfrom an aluminum material.